This invention relates to power transmission V-belts having a trapezoid cross-section and to a method of manufacturing the V-belts. More particularly, this invention relates to a power transmission V-belt comprising a tensile member arranged in the form of a layer along the center line of the belt, elastic rubber layers formed respectively on both surfaces of the layer of the tensile member, and fabric layers provided respectively on the surfaces of the elastic rubber layers. The invention also relates to a method of manufacturing the power transmission V-belt.
During the manufacture of V-belts, hardened scraps are created in the scraping step; that is, the material is uneconomically used. This invention has been developed mainly to eliminate this drawback. That is, the invention relates to a V-belt which is manufactured according to a belt blank having the layer of a tensile member along the center line thereof is cut into rings whereby direct molded belts having a trapezoid cross-section and indirect molded belts having an inverted trapezoid cross-section which are turned inside out before use are alternatively obtained. This invention is an improvement of that belt manufacturing method.
Belts of this type have been disclosed in U.S. Pat. Nos. 3,869,933 and 3,941,005, in which cord fabrics are provided on the upper and lower surface of the layer of a belt tensile member to increase the rigidity in the widthwise direction of the belt. This tends to prevent the belt from dropping in the pulley during running. However, these conventional belts are disadvantageous in that the cord fabrics are liable to peel off the layer of the tensile member because of a shearing stress applied to the belt. Also, the belt is relatively expensive.
In order to overcome this disadvantage, a belt has been proposed in U.S. Pat. No. 3,987,684, in which the same wide cross angle bias fabrics are arranged on the upper and lower surface layers of the belt, and short fibers are mixed in the both surfaces of the layer of the tensile member. This conventional belt is manufactured according to a method in which the layer of a tensile member is arranged along the center line of the belt and the same fabrics and the same rubber layers are symmetrically provided on the upper and lower surfaces of the layer of the tensile member, to form a sleeve-shaped vulcanized molded belt blank. The blank is cut into several rings, so that direct molded belts can be used as they are and indirect molded belts which must be turned inside out before use are also provided. However, it should be noted that the direct molded belt is different in performance from the indirect molded belt.
This can be ascertained with reference to FIG. 1 which is a sectional view of a sleeve-shaped vulcanized molded belt blank 7. The blank 7 is obtained according to a method in which a lower fabric 4, a lower rubber layer 6, the layer of a tensile member 2, an upper rubber layer 5 and an upper fabric 3 are laid on a cylindrical molding drum 1 in succession. The layer of the tensile member 2 is arranged along the center line thereof to form an assembly. The assembly is subjected to vulcanization. The circumferential length of the lower fabric 4 is shorter as much as 2.pi.t (where t is the thickness of the belt) than that of the upper fabric 3.
As shown in FIG. 2, the blank 7 is obliquely cut into rings to obtain direct molded belts and indirect molded belts. When the indirect molded belt 8 is turned inside out the lower fabric 4 is forcibly made longer by 2.pi.t than the upper fabric 3. In addition, when the indirect molded belt thus turned inside out is run on a small diameter pulley, the upper rubber layer and fabric on the layer of the tensile member is subjected to a tensile strain greater than the compression strain in the longitudinal direction of the lower member of the belt. That is, the upper member of the belt is strained more than the lower member.
As a result, the upper member of the belt may be cracked. It has been known that this crack occurs mainly in the upper fabric, or between the upper fabric and the rubber layer, but rarely occurs in the lower member of the belt. Thus, the conventional method is fatally disadvantageous in that the service life of the indirect molded belt is much shorter than that of the direct molded belt.